Actually, they can still be awesome slow cooked birds at that age. I have a large stovetop roaster pan with a domed lid (it is enameled metal) I put the cut up bird into it with 8-10 cups of broth and a handful of chunked carrots and celery and a few spices. I slow simmer it for 2 hrs, then make dumplings and drop the dumplings on top and let them cook for about 20 mins or so. The meat falls off of the bone and it is awesome with noodles or parsleyed potatoes.
I am at work right now so don't have my recipe available for exact amounts, if anyone is interested I can post the exact recipe after I'm home tomorrow.